【LeetCode】 263. Ugly Number

Description

Write a program to check whether a given number is an ugly number.

Ugly numbers are positive numbers whose prime factors only include 2, 3, 5.

Note:

• 1 is typically treated as an ugly number.
• Input is within the 32-bit signed integer range: [−2^31, 2^31 − 1].

寫一個程式去確認給予的數字是否為醜數。

醜數是指一個正整數它的質因數只有包含2、3、5。

注意：

• 1是一個醜數。
• 輸入數字是32位元的有號整數，其範圍為[−2^31, 2^31 − 1]。

Example:

Example 1:

Input: 6
Output: true
Explanation: 6 = 2 × 3
Example 2:

Input: 8
Output: true
Explanation: 8 = 2 × 2 × 2
Example 3:

Input: 14
Output: false 
Explanation: 14 is not ugly since it includes another prime factor 7.

Solution

• 用%(modulo)去判斷是否可以整除。
• 用while去不停地除。
• 記得判斷是否為整數。

Code

class Solution {
public:
    bool isUgly(int num) {
        if(num <= 0) return false;
        while(!(num % 2))
            num /= 2;
        while(!(num % 3))
            num /= 3;
        while(!(num % 5))
            num /= 5;
        return num == 1;
    }
};

tags: LeetCode C++